feat(KnowledgeManagement): 添加知识条目阅读功能

- 在知识集详情页面中添加阅读按钮，支持查看知识条目的内容
- 实现文本和Markdown格式知识条目的在线阅读预览
- 集成文件下载功能，支持从数据集文件中读取内容
- 添加内容长度限制，超过50000字符时截断并提示
- 使用模态框展示阅读内容，提供良好的用户体验
-

frontend/src/pages/KnowledgeManagement/Detail/KnowledgeSetDetail.tsx

@@ -6,10 +6,12 @@ import {
   Card,
   Descriptions,
   Empty,
+  Modal,
   Table,
   Tag,
+  Tooltip,
 } from "antd";
-import { DeleteOutlined, EditOutlined, PlusOutlined } from "@ant-design/icons";
+import { DeleteOutlined, EditOutlined, EyeOutlined, PlusOutlined } from "@ant-design/icons";
 import { useNavigate, useParams } from "react-router";
 import DetailHeader from "@/components/DetailHeader";
 import { SearchControls } from "@/components/SearchControls";
@@ -29,6 +31,7 @@ import {
 import {
   KnowledgeItem,
   KnowledgeSet,
+  KnowledgeContentType,
   KnowledgeStatusType,
 } from "../knowledge-management.model";
 import CreateKnowledgeSet from "../components/CreateKnowledgeSet";
@@ -36,6 +39,8 @@ import KnowledgeItemEditor from "../components/KnowledgeItemEditor";
 import ImportKnowledgeItemsDialog from "../components/ImportKnowledgeItemsDialog";
 import { formatDate } from "@/utils/unit";
 
+const MAX_READ_LENGTH = 50000;
+
 const KnowledgeSetDetail = () => {
   const navigate = useNavigate();
   const { message } = App.useApp();
@@ -44,6 +49,10 @@ const KnowledgeSetDetail = () => {
   const [showEdit, setShowEdit] = useState(false);
   const [itemEditorOpen, setItemEditorOpen] = useState(false);
   const [currentItem, setCurrentItem] = useState<KnowledgeItem | null>(null);
+  const [readItemId, setReadItemId] = useState<string | null>(null);
+  const [readModalOpen, setReadModalOpen] = useState(false);
+  const [readContent, setReadContent] = useState("");
+  const [readTitle, setReadTitle] = useState("");
 
   const fetchKnowledgeSet = useCallback(async () => {
     if (!id) return;
@@ -91,6 +100,55 @@ const KnowledgeSetDetail = () => {
     fetchData();
   };
 
+  const isReadableItem = (record: KnowledgeItemView) => {
+    return (
+      record.contentType === KnowledgeContentType.TEXT ||
+      record.contentType === KnowledgeContentType.MARKDOWN
+    );
+  };
+
+  const handleReadItem = async (record: KnowledgeItemView) => {
+    setReadItemId(record.id);
+    setReadTitle(record.title || "知识条目");
+
+    if (!record.sourceDatasetId || !record.sourceFileId) {
+      const content = record.content || "";
+      if (content.length > MAX_READ_LENGTH) {
+        setReadContent(
+          `${content.slice(0, MAX_READ_LENGTH)}\n\n... (内容过长，仅显示前 ${MAX_READ_LENGTH} 字符)`
+        );
+      } else {
+        setReadContent(content);
+      }
+      setReadModalOpen(true);
+      setReadItemId(null);
+      return;
+    }
+
+    const fileUrl = `/api/data-management/datasets/${record.sourceDatasetId}/files/${record.sourceFileId}/download`;
+
+    try {
+      const response = await fetch(fileUrl);
+      if (!response.ok) {
+        throw new Error("下载失败");
+      }
+      const text = await response.text();
+      if (text.length > MAX_READ_LENGTH) {
+        setReadContent(
+          `${text.slice(0, MAX_READ_LENGTH)}\n\n... (内容过长，仅显示前 ${MAX_READ_LENGTH} 字符)`
+        );
+      } else {
+        setReadContent(text);
+      }
+      setReadModalOpen(true);
+    } catch (error) {
+      console.error("读取知识条目失败", error);
+      message.error("读取失败，请稍后重试");
+    } finally {
+      setReadItemId(null);
+    }
+  };
+
   const statusMeta = knowledgeSet?.status
     ? knowledgeStatusMap[knowledgeSet.status]
     : undefined;
@@ -164,9 +222,19 @@ const KnowledgeSetDetail = () => {
     {
       title: "操作",
       key: "actions",
-      width: 140,
+      width: 200,
       render: (_: unknown, record: KnowledgeItemView) => (
         <div className="flex items-center gap-2">
+          <Tooltip title="阅读">
+            <Button
+              type="text"
+              icon={<EyeOutlined />}
+              onClick={() => handleReadItem(record)}
+              disabled={!isReadableItem(record)}
+              loading={readItemId === record.id}
+              aria-label="阅读"
+            />
+          </Tooltip>
           <Button
             type="text"
             icon={<EditOutlined />}
@@ -320,6 +388,35 @@ const KnowledgeSetDetail = () => {
           fetchData();
         }}
       />
+
+      <Modal
+        open={readModalOpen}
+        title={`阅读：${readTitle}`}
+        width={820}
+        onCancel={() => {
+          setReadModalOpen(false);
+          setReadContent("");
+          setReadTitle("");
+        }}
+        footer={[
+          <Button
+            key="close"
+            onClick={() => {
+              setReadModalOpen(false);
+              setReadContent("");
+              setReadTitle("");
+            }}
+          >
+            关闭
+          </Button>,
+        ]}
+      >
+        <pre
+          className="max-h-[520px] overflow-auto rounded bg-gray-50 p-4 text-xs whitespace-pre-wrap break-all"
+        >
+          {readContent}
+        </pre>
+      </Modal>
     </div>
   );
 };